This application claims the benefit of Korean Patent Application No. 48003/1996 filed Oct. 24, 1996, which is hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a method of forming a semiconductor device, and more particularly, to a method of forming a metal thin film. Although the present invention is suitable for a wide scope of applications, it is particularly suitable for forming a metal thin film used for a lower electrode in a high density memory device.
2. Discussion of the Related Art
Generally, a capacitor of a higher integrated DRAM is fabricated using a dielectric layer having a higher dielectric constant. However, if the dielectric layer is directly deposited on a polysilicon layer, the dielectric layer can easily react with silicon in the polysilicon layer. The reaction between the dielectric layer and the silicon eventually deteriorates an electrical characteristic of the capacitor.
To avoid such a problem, lower and upper electrodes of the DRAM capacitor are formed by a metal such as Pt, and a dielectric layer having a high-dielectric constant is formed between the electrodes. Using the platinum layer for the upper electrode is to prevent the dielectric layer from an undesirable reaction during heat treatment after formation of the capacitor. Further, Pt has a large work function and good reactivity with a dielectric layer having a higher dielectric constant such as PZT [Pb(Zr,Ti)O3] or BST [(Ba,Sr)TiO3].
A conventional method for forming a Pt thin film used for a memory will now be explained. FIGS. 1A to 1C are cross-sectional views showing a conventional method of forming a Pt thin film. As shown in FIG. 1A, a first Pt layer 12 for a lower electrode of a capacitor is formed on a semiconductor substrate 11.
Referring to FIG. 1B, a high dielectric layer 13 such as BST or PZT is formed on the first Pt layer 12, and then a heat treatment is carried out. As shown in FIG. 1C, a second Pt layer 14 for forming a upper electrode of the capacitor is formed on the dielectric layer 13.
Here, if the dielectric layer 13 is formed on the first Pt layer 12 and a heat treatment is performed, hillocks are locally formed between the first Pt layer 12 and the dielectric layer 13. The hillocks is resulted from the movement of Pt atoms in order to reduce an inner stress generated during the Pt layer formation process, or a heat treatment after the process. As a result, protrusions are formed on the surface of the Pt layer. Thus, the hillocks deteriorate an electrical characteristic of the device, or induce a breakdown at a lower electric field.
In other words, when the dielectric layer 13 is formed on the first Pt layer 12 and then a heat treatment is carried out, hillocks formed on the first Pt layer 12 penetrate the thin dielectric layer 13. Accordingly, the lower electrode of the capacitor directly comes into contact with the upper electrode.
As explained, the conventional method for forming a Pt thin film has the following problem. Since hillocks are locally formed on the lower electrode of the capacitor, a leakage current is generated and a breakdown is induced. As a result, the electrical characteristic of the device is significantly deteriorated.
Accordingly, the present invention is directed to a method for forming a Pt layer used for a memory that substantially obviates one or more of the problems due to limitations and disadvantages of the related art.
An object of the present invention is to provide a method of forming a Pt thin film used for a memory device, which controls the formation of hillocks in order to maximize the effective area of a capacitor and to remove the electrical deterioration due to the hillocks, thereby improving the electrical characteristic of the device.
Additional features and advantages of the invention will be set forth in the description which follows, and in part will be apparent from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims hereof as well as the appended drawings.
To achieve these and other advantages and in accordance with the purpose of the present invention, as embodied and broadly described, the method of forming a Pt thin film layer used for memory includes the steps of forming a Pt layer on a semiconductor substrate, forming uniform grains on the surface of the Pt layer, and forming a dielectric layer on the Pt layer on with the grains are formed, the dielectric layer having a high dielectric constant.
In another aspect of the present invention, a method of forming a metal thin film of a memory device having a capacitor, the method includes the steps of forming a metal layer on a semiconductor substrate, forming uniform grains on a surface of the metal layer, and forming a dielectric layer on the metal layer.
In another aspect of the present invention, a method of forming a metal thin film of a memory device having a capacitor includes the steps of forming a platinum layer on a substrate as a first electrode of the capacitor, bombarding external atoms against the surface of the platinum layer using plasma to form uniform grains, forming a dielectric layer on the platinum layer having uniform grains, and forming a second electrode on the dielectric layer.
In another aspect of the present invention, a method of forming a metal thin film of a memory device having a capacitor includes the steps of forming a platinum layer on a substrate as a first electrode of the capacitor, etching a surface of the platinum layer using an etching gas to form uniform grains on the surface, forming a dielectric layer on the platinum layer, and forming a second electrode on the dielectric layer.
In another aspect of the present invention, a method of forming a metal thin film of a memory device having a capacitor includes the steps of forming a platinum layer on a substrate as a first electrode of the capacitor, forming a reaction layer on the platinum layer, heating the reaction layer and the platinum layer to diffuse the reaction layer into the platinum layer, removing the reaction layer, and forming a dielectric layer on the platinum layer.
In a further aspect of the present invention, a method of forming a metal thin film of a memory device having a capacitor includes the steps of forming a Pt layer on a substrate as a first electrode of a capacitor, forming a hillock formation stop layer on the Pt layer, then carrying out heat treatment, forming a dielectric layer on the hillock formation stop layer, and forming a second electrode of the capacitor on the dielectric layer.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory and are intended to provide further explanation of the invention as claimed.